Method for reducing the level of elemental sulfur and total sulfur in hydrocarbon streams

ABSTRACT

A method for reducing the level of elemental sulfur from sulfur-containing hydrocarbon streams as well as reducing the level of total sulfur in such streams. Preferred hydrocarbon streams include fuel streams such as naphtha streams that are transported through a pipeline. The sulfur-containing hydrocarbon stream is contacted with a mixture of water, a caustic, at least one metal sulfide, and an aromatic mercaptan. This results in an aqueous phase and a hydrocarbon phase containing reduced levels of both elemental sulfur and total sulfur.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of U.S. Provisional Patent Application Serial No. 60/258,587 filed Dec. 28, 2000.

FIELD OF THE INVENTION

[0002] This invention relates to a method for reducing the level of elemental sulfur from sulfur-containing hydrocarbon streams as well as reducing the level of total sulfur in such streams. Preferred hydrocarbon streams include fuel streams such as naphtha streams that are transported through a pipeline. The sulfur-containing hydrocarbon stream is contacted with a mixture of water, a caustic, at least one metal sulfide, and an aromatic mercaptan. This results in an aqueous phase and a hydrocarbon phase containing reduced levels of both elemental sulfur and total sulfur.

BACKGROUND OF THE INVENTION

[0003] It is well known that elemental sulfur in hydrocarbon streams, such as petroleum streams, is corrosive and damaging to metal equipment. Elemental sulfur and sulfur compounds may be present in varying concentrations in refined petroleum streams, such as in gasoline boiling range streams. Additional contamination will typically take place as a consequence of transporting the refined stream through pipelines that contain sulfur contaminants remaining in the pipeline from the transportation of sour hydrocarbon streams, such as petroleum crudes. The sulfur also has a particularly corrosive effect on equipment, such as brass valves, gauges and in-tank fuel pump copper commutators.

[0004] Various techniques have been reported for removing elemental sulfur from petroleum streams. For example, U.S. Pat. No. 4,149,966 discloses a method for removing elemental sulfur from refined hydrocarbon fuel streams by adding an organo-mercaptan compound plus a copper compound capable of forming a soluble complex with the mercaptan and sulfur. The fuel is contacted with an adsorbent material to remove the resulting copper complex and substantially all the elemental sulfur.

[0005] U.S. Pat. No. 4,011,882 discloses a method for reducing sulfur contamination of refined hydrocarbon fluids transported in a pipeline for the transportation of sweet and sour hydrocarbon fluids by washing the pipeline with a wash solution containing a mixture of light and heavy amines, a corrosion inhibitor, a surfactant and an alkanol containing from 1 to 6 carbon atoms.

[0006] U.S. Pat. No. 5,618,408 teaches a method for reducing the amount of sulfur and other sulfur contaminants picked-up by refined hydrocarbon products, such as gasoline and distillate fuels, that are pipelined in a pipeline used to transport heavier sour hydrocarbon streams. The method involves controlling the level of dissolved oxygen in the refined hydrocarbon stream that is to be pipelined.

[0007] The removal of elemental sulfur from pipelined fuels is also addressed in U.S. Pat. No. 5,250,181 which teaches the use of an aqueous solution containing a caustic, an aliphatic mercaptan, and optionally a sulfide to produce an aqueous layer containing metal polysulfides and a clear fluid layer having a reduced elemental sulfur level. U.S. Pat. No. 5,199,978 teaches the use of an inorganic caustic material, an alkyl alcohol, and an organo mercaptan, or sulfide compound, capable of reacting with sulfur to form a fluid-insoluble polysulfide salt reaction product at ambient temperatures.

[0008] Also, U.S. Pat. No. 5,160,045 teaches that the addition of a sulphide to an alkali solution can remove elemental sulfur from hydrocarbon fluids and U.S. Pat. No. 5,250,180 teaches that the addition of an aliphatic mercaptan and a sulphide to an alkali solution can remove elemental sulfur from hydrocarbon fluids. U.S. Pat. No. 2,460,227 teaches that the addition of Na₂S and an aromatic mercaptan at relatively high concentrations to an alkali solution can remove elemental sulfur from hydrocarbon fluids. However, none of these patents teach the reduction of total sulfur in the hydrocarbon stream while also reducing the elemental sulfur content. In fact, the addition of a sulfur containing species, such as a mercaptan, to the feed under certain conditions results in an increase in total sulfur in the product stream.

[0009] While such methods have met with varying degrees of success, there still exists a need in the art for a method capable of reducing the total sulfur content of a hydrocarbon stream while reducing the elemental sulfur content as well.

SUMMARY OF THE INVENTION

[0010] In accordance with the present invention there is provided a method for reducing both the level of elemental sulfur and total sulfur of a hydrocarbon stream containing same, which method comprises: a) mixing with said stream, water, a caustic, at least one metal sulfide, and at least one aromatic mercaptan, thereby resulting in a hydrocarbon phase and an aqueous phase, wherein said mixture is used in an effective amount and under effective conditions so that the elemental sulfur reacts with said at least one metal sulfide to form the corresponding metal polysulfide that is soluble in the aqueous phase; and b) separating said aqueous phase containing said metal polysulfide component, and the hydrocarbon phase that is substantially reduced in both elemental sulfur and total sulfur.

[0011] In a preferred embodiment, the aromatic mercaptan is present in a range from about 1 to about 1000 wppm.

[0012] In another preferred embodiment, the aromatic mercaptan is added to the hydrocarbon stream.

[0013] In yet another preferred embodiment, the aromatic mercaptan is added to the aqueous phase.

[0014] In another preferred embodiment of the present invention the hydrocarbon stream is a naphtha boiling range stream.

[0015] In still another preferred embodiment of the present invention the caustic is an inorganic caustic represented by the formula MOH where M is selected from the group consisting of lithium, sodium, potassium, NH₄, and mixtures thereof.

[0016] In another preferred embodiment of the present invention the sulfide is of a metal selected from Groups I and II of the Periodic Table of the Elements.

[0017] In yet other preferred embodiments of the present invention the aromatic mercaptan is selected from the group consisting of thiophenol, ethyl thiophenol, methyoxythiophenol, dimethylthiophenol, napthalenethiols, phenyl-di-mercapatan, and thiocresol.

DETAILED DESCRIPTION OF THE INVENTION

[0018] Hydrocarbon streams that are treated in accordance with the present invention are preferably petroleum refinery hydrocarbon streams containing elemental sulfur, particularly those naphtha and distillate streams wherein the sulfur has been picked-up when the stream is transported through a pipeline. Preferred streams are also those wherein the elemental sulfur is detrimental to the performance of the intended use of the hydrocarbon stream. The more preferred streams to be treated in accordance with the present invention are naphtha boiling range streams that are also referred to as gasoline boiling range streams. Naphtha boiling range streams can comprise any one or more refinery streams boiling in the range from about 10° C. to about 230° C., at atmospheric pressure. The naphtha stream generally contains cracked naphtha that typically comprises fluid catalytic cracking unit naphtha (FCC catalytic naphtha, or cat cracked naphtha), coker naphtha, hydrocracker naphtha, resid hydrotreater naphtha, debutanized natural gasoline (DNG), and gasoline blending components from other sources from which a naphtha boiling range stream can be produced. FCC catalytic naphtha and coker naphtha are generally more olefinic naphthas since they are products of catalytic and/or thermal cracking reactions. Non-limiting examples of hydrocarbon feed streams boiling in the distillate range include diesel fuels, jet fuels, kerosene, heating oils, and lubes. Such streams typically have a boiling range from about 150° C. to about 600° C., preferably from about 175° C. to about 400° C. Dialkyl ether streams may also be treated in accordance with this invention. Alkyl ethers are typically used to improve the octane rating of gasoline. These ethers are typically dialkyl ethers having 1 to 7 carbon atoms in each alkyl group. Illustrative ethers are methyl tertiary-butyl ether, methyl tertiary-amyl ether, methyl tertiary-hexyl ether, ethyl tertiary-butyl ether, n-propyl tertiary-butyl ether, and isopropyl tertiary-amyl ether. Mixtures of these ethers and hydrocarbon streams may also be treated in accordance with this invention.

[0019] The hydrocarbon streams can contain quantities of elemental sulfur as high as 1000 mg sulfur per liter, typically from about 10 to about 100 mg per liter, more typically from about 10 to 60 mg per liter, and most typically from about 10 to 30 mg per liter. Such streams can be effectively treated in accordance with this invention to reduce the elemental sulfur contamination to less than about 10 mg per liter, preferably to less than about 5 mg sulfur per liter, or lower.

[0020] The inorganic caustic material that is employed in the practice of this invention includes alkali metal or ammonium hydroxides having the formula MOH wherein M is selected from the group consisting of lithium, sodium, potassium, NH₄, or mixtures thereof. M is preferably sodium or potassium, more preferably sodium.

[0021] The sulfide that is used in the practice of the present invention includes mono sulfides and polysulfides of metals from Groups 1a and 2a of the Periodic Table of the Elements, such as the one found in the inside front cover of the 55^(th) edition of the Handbook of Chemistry and Physics, 1974-1975, CRC Press. Group 1a metals include Li, Na, and K; and Group 2a metals include Be, Mg, and Ca. Examples of such sulfides include Na₂S, K₂S, Li₂S, NaHS, (NH₄)₂S, and the like. Na₂S is preferred. The sulfide in caustic reacts with the elemental sulfur in the hydrocarbon stream to be treated to form polysulfides in caustic. The sulfide may be present in a convenient source of caustic such as white liquor from paper pulp mills. Thus, the elemental sulfur moves from the hydrocarbon stream to the aqueous caustic phase.

[0022] Aromatic mercaptans are employed in the practice of the present invention to improve performance. These mercaptans, in the presence of caustic, form a sulfur complex that transfers easily into the fuel to react with the elemental sulfur, thereby accelerating sulfur removal from the hydrocarbon stream. The aromatic mercaptans that may be used in the practice of the present invention include a wide variety of compounds having the general formula RSH, where R represents an aromatic group. Non-limiting examples of such aromatic mercaptans include: thiophenol, ethyl thiophenol, methyoxythiophenol, dimethylthiophenol, napthalenethiols, phenyl-di-mercaptans, and thiocresol. Most preferred is thiophenol.

[0023] The proportion of water, caustic, sulfide and aromatic mercaptan is an effective amount that will allow a predetermined quantity of elemental sulfur to react with the sulfide and enters the aqueous phase. This proportion may vary within wide limits. Typically, the aqueous treating solution contains caustic in the range of about 0.01 to 20M, with the sulfide concentration being from about 0.1 wt. % to about 5 wt. %, preferably 0.2 wt. % to 2 wt. %. The amount of aromatic mercaptan will be from about 1 wppm to about 1,000 wppm, preferably from about 1 wppm to about 100 wppm in either the caustic or hydrocarbon stream. The relative amount of aqueous treating solution containing caustic, metal sulfide, and optionally the aromatic mercaptan and the hydrocarbon stream to be treated may also vary within wide limits. Usually from about 0.05 to about 10, preferably from about 0.1 to about 1.0 volumes of aqueous treating solution will be used per volume of hydrocarbon stream to be treated.

[0024] The reactants may be dispersed within the hydrocarbon stream by any suitable mixing device that will provide adequate mixing. The caustic phase, or immiscible treatment solution, must be the continuous phase while the hydrocarbon stream must be the dispersed phase. Having the hydrocarbon phase as the dispersed phase ensures a large surface area for the extraction of elemental sulfur into the aqueous caustic phase. Thereafter, the mixture is allowed to settle to produce the aqueous and hydrocarbon stream layers.

[0025] Treating conditions that can be used in the practice of the present invention are effective conditions in the conventional range. That is, the contacting of the hydrocarbon stream to be treated is preferably effected at ambient temperature conditions, although higher temperatures up to about 100° C., or higher, may be used. Substantially atmospheric pressures are suitable, although higher pressures may, for example, range up to about 1,000 psig. Contact times may also vary widely depending on the hydrocarbon stream to be treated, the amount of elemental sulfur therein, and the composition the treating solution. The contact time should be chosen to affect the desired degree of elemental sulfur conversion. The reaction proceeds relatively fast, usually within several minutes, depending on solution strengths and compositions. Contact times will range from about 30 seconds to a few hours.

[0026] In general, the process of the present invention involves the addition to the hydrocarbon stream to be treated a mixture of effective amounts of caustic, water, sulfide, and aromatic mercaptan. The mixture is allowed to settle so as to form an aqueous layer containing metal polysulfides and a clear hydrocarbon stream layer having a reduced level of both elemental sulfur and total sulfur. The treated hydrocarbon stream can be recovered by any suitable liquid/liquid separation technique, such as by decantation or distillation. The recovered aqueous layer may be recycled back to the mixing zone for contact with the hydrocarbon stream to be treated, or it may be discarded or used, for example, as a feedstock to pulping paper mills, such as those employing the Kraft pulp mill process.

[0027] The instant invention will typically be practiced by blending an immiscible water/alkali-metal/sulfide mixture with the sulfur-containing hydrocarbon stream to be treated. An effective amount of aromatic mercaptan is added to either the hydrocarbon phase or the aqueous phase for improved performance. The hydrocarbon and aqueous solutions are blended in a mixing device such that the immiscible aqueous solution constitutes the continuous phase of the mixture and the hydrocarbon stream constitutes the dispersed phase.

[0028] The sulfide concentration in the aqueous solution is from about 0.1 wt. % to about 5 wt. %, or as allowed by precipitation limits.

[0029] The following examples are illustrative of the invention and are not to be taken as limiting in any way.

EXAMPLE 1 (Comparative)

[0030] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass vessel was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 0° C. First, 217 ml of 25 Be of caustic and then 433 ml of gasoline containing 9 mg/l of elemental sulfur (S°) was added to the glass vessel. Be refers to the Baume scale which is a hydrometer scale that measures the specific gravity of liquids. A Baume or Be of 25 is equivalent to a specific gravity of 1.208 g/cc. After the contents of the glass vessel reached 0° C., 63 wppm propyl mercaptan (propyl mercaptan: S° ratio of 2 moles to 1 mole (2.0 m/m)) was injected into the hydrocarbon (gasoline) phase. The mixer was then started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run, the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

EXAMPLE 2 (Comparative)

[0031] The procedure in Example 1 was followed except that no propyl mercaptan was added.

[0032] Table 1 clearly demonstrates that the aliphatic mercaptan, propyl mercaptan, significantly improves the elemental sulfur conversion performance. However, there is no total sulfur removal. In fact, the product contains more sulfur than the feed (i.e., negative sulfur removal) due the formation of dipropyl disulphide and dipropyl trisulphides originating from the propyl mercaptan injected into the feed. These compounds are soluble in gasoline. TABLE 1 Effect of Organic Mercaptan on Elemental Sulfur Conversion and Sulfur Removal (0° C., 50% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 2 Example 1 (Run #) Feed (3) (2) Mercaptan Type None Propyl mercaptan Mercaptan Concentration wppm 0 63 m/m 0 2 Mercaptan Phase addition None Hydrocarbon Product Sulphur S°, mg/l 9.3 11.9 0 Total S, mg/l 50 60 51 Propyl mercaptan, mg/l 0 0 0 Dipropyl disulphide, mg/l 0 0 3.9 Dipropyl trisulphide, mg/l 0 0 1.9 S°, Converted, %* −20 100 S Removed, % Max** −108 −11

[0033] Example 1 in Table 1 also clearly demonstrates that removing 100% of elemental sulfur does not guarantee that the total sulfur level in the product will be reduced. In fact, these data indicate that the mechanism for reducing the elemental sulfur in the product is not the same as that for reducing the total sulfur level in the treated product. cl EXAMPLE 3 (Comparative)

[0034] The procedure of Example 1 above was followed except the caustic contained 1 wt. % Na₂S and 32 wppm of propyl mercaptan (propyl mercaptan: S° ratio of 1.0 m/m) was injected in the hydrocarbon phase instead of 63 wppm of propyl mercaptan. The results are shown in Table 2 below.

EXAMPLE 4 (Comparative)

[0035] The procedure of Example 3 above was followed except the caustic contained 2 wt. % Na₂S and 63 wppm of propyl mercaptan (propyl mercaptan: S° ratio of 2.0 m/m) was used.

[0036] As shown in Table 2 below, the addition of Na2S to the caustic phase with propyl mercaptan added to the hydrocarbon phase, significantly improves the sulfur removal performance (−11 to 22%) while maintaining a 100% elemental sulfur conversion. However, at 2 wt. % Na₂S an organic sulphonate precipitate forms in the caustic solution which raises major operational concerns (i.e., plugging of reactor and separation vessels). These data indicate for the conditions defined in Table 2 no precipitate is formed at less than 2 wt. % of the sulfide additive. However, since the exact sulfide concentration leading to the formation of a precipitate depends on the operating conditions higher limits are possible at other conditions. TABLE 2 Effect of Na₂S and Propyl Mercaptan on Elemental Sulfur Conversion and Sulfur Removal (Gasoline feed: 9.3 mg/l S°, 50 mg/l total sulfur, 0° C., 50% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 1 Example 3 Example 4 (Run #) (2) (4) (7) Mercaptan Type Propyl Propyl Propyl mercaptan mercaptan mercaptan Mercaptan Concentration wppm 63 32 63 m/m 2 1 2 Mercaptan Phase addition Hydrocarbon Hydrocarbon Hydrocarbon Na₂S, wt % 0 1 2 Precipitate Formed No No Yes Prod S°, mg/l 0 0 0 Prod Total S, mg/l 51 48 46 S° Converted, % 100 100 100 S Removed, % Max −11 22 43

EXAMPLE 5 (Comparative)

[0037] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 15° C. First, 325 ml of 25 Be caustic containing 0.7 wt. % Na₂S and then 325 ml of gasoline containing 24 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel reached 15° C., 25 wppm propyl mercaptan (propyl mercaptan: S° ratio of 0.3 m/m) was injected into the hydrocarbon phase. The mixer was then started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

EXAMPLE 6

[0038] The procedure of Example 5 above was followed except 21 wppm of thiophenol (aromatic mercaptan) was added into the caustic phase instead of 25 wppm of propyl mercaptan being added to the hydrocarbon phase.

[0039] As shown in Table 3 adding thiophenol, an aromatic mercaptan, to the caustic phase instead of propyl mercaptan, an aliphatic mercaptan, to the hydrocarbon phase significantly improves the sulfur removal performance while maintaining a 100% elemental sulfur conversion. TABLE 3 Effect of Propyl Mercaptan in the Mogas Phase and Thiophenol in the Caustic Phase on Elemental Sulfur Conversion and Sulfur Removal (Gasoline feed: 24.2 mg/l S°, 60 mg/l total sulfur, 15° C., 100% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 5 Example 6 (Run #) (68) (67) Mercaptan Type Propyl mercaptan Thiophenol Mercaptan Concentration wppm 25 21 m/m 0.3 0.3 Mercaptan Phase addition Hydrocarbon Caustic Na₂S, wt % 0.7 0.7 Precipitate Formed No No Prod S°, mg/l 0 0 Prod Total S, mg/l 51 46 S° Converted, % 100 100 S Removed, % Max 37 58

EXAMPLE 7 (Comparative)

[0040] The procedure of Example 5 above was followed except the glass vessel was placed in a constant temperature bath set at 20° C. and 10 wppm propyl mercaptan (propyl mercaptan: S° ratio of 0.2 m/m) was added to the caustic phase.

EXAMPLE 8

[0041] The procedure of Example 7 above was followed except that 14 wppm thiophenol (thiophenol: S° ratio of 0.2 m/m) was added to the caustic phase.

[0042] As shown in Table 4 below, adding thiophenol, an aromatic mercaptan, instead of propyl mercaptan, an aliphatic mercaptan, to the caustic phase significantly improves the sulfur removal performance while maintaining a 100% elemental sulfur conversion. TABLE 4 Effect of Propyl Mercaptan and Thiophenol in the Caustic Phase on Elemental Sulfur Conversion and Sulfur Removal (Gasoline feed: 24.2 mg/l S°, 60 mg/l total sulfur, 20° C., 100% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 7 Example 8 (Run #) (71) (69) Mercaptan Type Propyl mercaptan Thiophenol Mercaptan Concentration wppm 10 14 m/m 0.2 0.2 Mercaptan Phase addition Caustic Caustic Na₂S, wt % 0.7 0.7 Precipitate Formed No No Prod S°, mg/l 0 0 Prod Total S, mg/l 51 45 S° Converted, % 100 100 S Removed, % Max 37 62

EXAMPLE 9 (Comparative)

[0043] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 0° C. First, 433 ml of 25 Be caustic containing 2 wt. % Na₂S and then 217 ml of gasoline containing 9 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel reached 0° C. the mixer was then started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

EXAMPLE 10

[0044] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 3° C. First, 325 ml of 25 Be caustic containing 1 wt. % Na₂S and 103 wppm thiophenol (thiophenol: S° ratio of 1.5 m/m) and then 325 ml of gasoline containing 24 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel reached 3° C. the mixer was started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

EXAMPLE 11

[0045] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 30° C. First, 325 ml of 25 Be caustic containing 200 wppm thiophenol (thiophenol: S° ratio of 2.9 m/m) and then 325 ml of gasoline containing 24 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel reached 30° C. the mixer was started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

[0046] Table 5 shows that adding thiophenol to a Na₂S-caustic solution significantly improves both the elemental sulfur conversion and sulfur removal performance. In fact, for sulfur removal with the combination of thiophenol and Na₂S is better than with the addition of each additive on its own. TABLE 5 Effect of Aromatic Mercaptan and Na₂S (25 Be caustic, 1000 rpm, 20 min) Example 9 Example 10 Example 11 (Run #) (8) (84) (33) Temperature, ° C. 0 3 30 Feed S°, mg/l 9.3 24.2 24.2 Treat Rate, % 50 100 100 Mercaptan Type None Thiophenol Thiophenol Mercaptan Concentration wppm 0 103 200 m/m 0 1.5 2.9 Mercaptan Phase addition None Caustic Caustic Na₂S, wt % 2 1 0 Precipitate Formed No No No Prod S°, mg/l 2.8 0 0 Prod Total S, mg/l 54 45 64 S° Converted, % 69.9 100 100 S Removed, % Max −43 62 −17

EXAMPLE 12

[0047] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 15° C. First, 325 ml of 25 Be caustic containing 1 wt. % Na₂S and 35 wppm of thiophenol (thiophenol: S° ratio of 0.5 m/m) and then 325 ml of gasoline containing 24 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel reached 15° C. the mixer was started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

EXAMPLE 13

[0048] A 1 liter-4″ diameter glass vessel with 4 vertical baffles was first purged with nitrogen to displace any oxygen. A six-blade turbine mixer (1.5″ diameter) situated in the center of the glass was preset at 1000 rpm. The glass vessel was placed in a constant temperature bath set at 15° C. First, 325 ml of 25 Be caustic containing 1 wt. % Na₂S and then 325 ml of gasoline containing 24 mg/l of elemental sulfur (S°) was added to the glass vessel. After the contents of the glass vessel re ached 15° C. 60 wppm of thiophenol (thiophenol: S° ratio of 0.5 m/m) was injected into the hydrocarbon phase. The mixer was then started and the run time was set at zero. This operation was allowed to continue for 20 minutes after which time a hydrocarbon sample was taken and washed with de-ionized water to quench the reaction (the water-hydrocarbon mixture was shaken vigorously for 30 seconds). After the run the vessel and mixer were cleaned with de-ionized water and dried to remove any traces of caustic and residual products.

[0049] As shown in Table 6 there was no difference in the elemental sulfur conversion and sulfur reduction between adding thiophenol to the caustic or the gasoline phase. TABLE 6 Effect of Phase Addition of Aromatic Mercaptan (Gasoline feed: 24.2 mg/l S°, 60 mg/l total sulfur, 15° C., 100% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 12 Example 13 (Run #) (79) (81) Mercaptan Type Thiophenol Thiophenol Mercaptan Concentration wppm 35 60 m/m 0.5 0.5 Mercaptan Phase addition Caustic Gasoline Na₂S, wt % 1 1 Precipitate Formed No No Prod S°, mg/l 0 0 Prod Total S, mg/l 43 43 S° Converted, % 100 100 S Removed, % Max 70 70

EXAMPLE 14

[0050] The procedure of Example 12 above was followed except the constant temperature bath was set at 30° C. and 2.0 wt. % thiophenol (thiophenol: S° ratio of 290 m/m) was used instead of 35 wppm of thiophenol.

EXAMPLE 15

[0051] The procedure of Example 14 above was followed except that 20 wppm of thiophenol (thiophenol: S° ratio of 0.3 m/m) was used.

[0052] As shown in Table 7 below increasing the aromatic mercaptan (thiophenol) concentration in the caustic phase from 20 to 20000 wppm significantly reduces the sulfur removal performance. Although elemental sulfur is still removed at the high aromatic mercaptan concentrations the total sulfur removal is negative due to the high level of diphenyl disulphide and diphenyl trisulphide in the product originating from the aromatic mercaptan injected into the feed. These compounds are soluble in gasoline. TABLE 7 Effect of Thiophenol Concentration (Gasoline feed: 24.2 mg/l S°, 60 mg/l total sulfur, 30° C., 100% treat rate, 25 Be caustic, 1000 rpm, 20 min) Example 14 Example 15 (Run #) (35) (31) Mercaptan Type Thiophenol Thiophenol Mercaptan Concentration wppm 20 20000 m/m 0.3 290 Mercaptan Phase addition Caustic Caustic Na₂S, wt % 1 1 Precipitate Formed No No Product Sulfur S°, mg/l 0 0 Total S, mg/l 44 73 diphenyl disulphide, mg/l 6 40 S° Converted, % 100 100 S Removed, % Max 66 −54 

What is claimed is:
 1. A method for reducing both the level of elemental sulfur and total sulfur of a hydrocarbon stream containing same, which method comprises: a) mixing with said stream, water, a caustic, at least one metal sulfide, and at least one aromatic mercaptan, thereby resulting in a hydrocarbon phase and an aqueous phase, wherein said mixture is used in an effective amount and under effective conditions so that the elemental sulfur reacts with said at least one metal sulfide to form the corresponding metal polysulfide that is soluble in the aqueous phase; and b) separating said aqueous phase containing said metal polysulfide component, and said hydrocarbon phase that is substantially reduced in both elemental sulfur and total sulfur.
 2. The method of claim 1 wherein the hydrocarbon stream is a naphtha boiling range stream.
 3. The method of claim 1 wherein the caustic is represented by the formula MOH where M is selected from the group consisting of lithium, sodium, potassium, NH₄, and mixtures thereof.
 4. The method of claim 3 wherein the caustic is used in the range of about 0.01 to 20 molar.
 5. The method of claim 1 wherein the sulfide is of a metal selected from Groups 1a and 2a of the Periodic Table of the Elements.
 6. The method of claim 5 wherein the sulfide is selected from the group consisting of Na₂S, K₂S, Li₂S, NaHS, (NH₄)₂S, and mixtures thereof.
 7. The method of claim 5 wherein the sulfide is used in range of about 0.1 wt. % to about 5 wt. %.
 8. The method of claim 1 wherein the aromatic mercaptan is selected from the group consisting of thiophenol, ethyl thiophenol, methyoxythiophenol, dimethylthiophenol, naphtalenethiols, phenyl-di-mercapatan, and thiocresol.
 9. The method of claim 7 wherein the aromatic mercaptan is present in a range from about 1 to about 1000 wppm.
 10. The method of claim 1 wherein the aromatic mercaptan is added to the hydrocarbon stream.
 11. The method of 1 wherein the aromatic mercaptan is added to the aqueous phase.
 12. The method of claim 1 wherein the aqueous phase is from about 0.05 to about 10 times the volume of the hydrocarbon phase.
 13. The method of claim 12 wherein the aqueous phase is from about 0.1 to about 10 times the volume of the hydrocarbon phase.
 14. A method for reducing both the level of elemental sulfur and total sulfur of a hydrocarbon stream containing same, which method comprises: a) mixing with said stream, water, a caustic represented by the formula MOH where M is selected from the group consisting of lithium, sodium, potassium, NH₄, and mixtures thereof, at least one metal sulfide of a metal selected from Groups 1a and 2a of the Periodic Table of the Elements, and at least one aromatic mercaptan, thereby resulting in a hydrocarbon phase and an aqueous phase, wherein said mixture is used in an effective amount and under effective conditions so that the elemental sulfur reacts with said at least one metal sulfide to form the corresponding metal polysulfide that is soluble in the aqueous phase; and b) separating said aqueous phase containing said metal polysulfide component, and said hydrocarbon phase that is substantially reduced in both elemental sulfur and total sulfur.
 15. The method of claim 14 wherein the hydrocarbon stream is a naphtha boiling range stream.
 16. The method of claim 14 wherein the caustic is used in the range of about 0.01 to 20 molar.
 17. The method of claim 14 wherein the sulfide is selected from the group consisting of Na₂S, K₂S, Li₂S, NaHS, (NH₄)₂S, and mixtures thereof.
 18. The method of claim 17 wherein the sulfide is used in range of about 0.1 wt. % to about 5 wt. %.
 19. The method of claim 14 wherein the aromatic mercaptan is selected from the group consisting of thiophenol, ethyl thiophenol, methyoxythiophenol, dimethylthiophenol, naphtalenethiols, phenyl-di-mercapatan, and thiocresol.
 20. The method of claim 19 wherein the aromatic mercaptan is present in a range from about 1 to about 1000 wppm.
 21. The method of claim 14 wherein the aromatic mercaptan is added to the hydrocarbon stream.
 22. The method of 14 wherein the aromatic mercaptan is added to the aqueous phase.
 23. The method of claim 14 wherein the aqueous phase is from about 0.05 to about 10 times the volume of the hydrocarbon phase.
 24. The method of claim 23 wherein the aqueous phase is from about 0.1 to about 10 times the volume of the hydrocarbon phase. 